1. Field of the Invention
The present invention relates to a printing cylinder for a rotary printing press with a jacket including a plurality of coaxial tubes, in particular a resilient interior tube, a filler body outside of the interior tube and a printing forme support on the outside of the filler body.
2. Description of Background and Material Information
Printing cylinders of the aforementioned type are employed in rotary printing presses of different types, in particular for rotogravure printing, flatbed printing, including offset printing, letterpress printing, including flexographic printing, and for embossing a web of material. As a rule, such printing cylinders act together with an impression cylinder on a web of material, for example made of paper, a printable or embossable foil of plastic or metal, or a fiber material for transferring the pattern of the printing cylinder to the web of material by means of ink or by embossing.
A printing cylinder of the aforementioned type is known, for example, from European Published Patent Application No. 0,384,104, published on Aug. 29, 1990. In this case the resilient inner body is wound from fiberglass-reinforced plastic. The filler body consists of foamed polyurethane, and the printing forme support of an electroplated copper layer or an engravable photo-polymer, on the surface of which the pattern to be printed is applied.
As a rule, the jacket of the printing cylinder is connected with a driven shaft which rotates along with it, such as disclosed in Dutch Published Patent Application No. 8,302,811, published on Mar. 1, 1985. To change the printing press to another diameter, i.e., another register or another format, it is necessary either to exchange the printing cylinder for one with an appropriate diameter or the jacket has to be separated from the shaft and pulled off, which often can only be done with difficulty.
A printing cylinder is known from British Published Patent Application No. 2,051,681, published on Jan. 21, 1981, or German Patent No. 2,700,118, published on Jul. 14, 1977, where the inner part of the jacket is embodied as a pressure-tight hollow cylinder, which is provided at its two ends with journals which rotate along with it. The outer concentric jacket layer which supports the print backing is seated frictionally engaged on the inner part of the jacket. If needed, it can be separated from the inner part by means of gas under pressure, which is brought via bores from the inner part of the jacket into the space between the inner part of the jacket and the outer part. However, the removal of the outer part of the jacket presents difficulties here too, because of the considerable loss of pressure gas and the uneven expansion of the outer part.
When printing ever wider webs and correspondingly using ever longer printing cylinders, particularly when keeping the format, i.e., with an increase of the length-diameter ratio from a value of 10:1, customary up to now, to values of 15:1 or more, it also becomes problematical to achieve an even printing quality over the entire width of the web. This would require an even distribution of pressure, at least over the utilized length of the printing cylinder. Attempts have already been made to embody the counter-pressure roller or the impression cylinder cooperating with the printing cylinder in such a way that the latter exerts a printing pressure on the printing cylinder or the web to be imprinted, which can be at least partially individually adjusted over the web width or cylinder length. This is often sufficient to achieve the desired print quality with smaller rotary printing presses having shorter printing cylinders.
With greater printing width and correspondingly longer printing cylinders the pressure can be maintained evenly with appropriately embodied impression cylinders. But the sagging of the printing cylinder caused by the pressure is sufficiently great that the ink application over the width of the roller and possibly the scraping off of the ink by the doctor blades over the width become uneven, because as a rule the ink roller and the doctor blade cannot follow the bending of the printing cylinder to the required degree. This causes register fluctuations, color fluctuations and the formation of creases in the web of material. Thus, there is insufficient assurance of an even printing pressure over the width alone in case of wider printing presses.
With longer printing cylinders for web widths up to the range of approximately 10 meters, the change to another register and the exchange of the printing forme support by pulling off the outer part of the cylinder jacket can not be accomplished by means of the known methods.